Precise recognition of Fe3+ in a biological system and ecological environment is of great importance. Therefore, a new phenanthroimidazole based chemosensor SP (H2 saldien-substituted phenanthroimidazole) was designed, fabricated and evaluated as a facile fluorogenic “OFF-ON” type chemosensor toward Fe3+ in aqueous solution. The SP could sensitively and selectively recognize Fe3+ with a limit of detection of 0.36 µM. The sensing mechanism for the SP-Fe3+ system was successfully proven on FT-IR spectroscopy, TOF-MS and the calculations of DFT (density functional theory). It is found that the SP could be basically recycled through treating with EDTA. Moreover, Fe3+ can be visualized by prepared SP in the test kit and low-cost smartphone sensor applications. Evidently, the experiments manifested that the prepared SP was capable of recognizing of Fe3+ in aqueous media.